This invention relates to semiconductor type optically activated high voltage, high power switches. Such switches have been developed for use in kilovolt pulser circuits for producing high power pulses with rapid rise and fall times. These optical switches may comprise, for example, a bulk semiconductor wafer with a pair of spaced contacts applied to one of the broad surfaces thereof to define a gap between the contacts. The gap length is chosen to provide a hold-off voltage higher than the voltage to be switched, which is applied across the gap. Application of light energy to the gap area which is sufficiently energetic to cause the formation of charge carriers in the form of electrons and holes (or pairs), will rapidly close the switch and apply the high voltage to a load in series therewith. If the light covers the entire gap area, there is no transit time limitation and the switching action is extremely fast. Also, the switching is accomplished with a low jitter, and has the capability of high pulse repetition frequencies. These switches can also be used as opening switches in which the light activation is rapidly removed to rapidly break the circuit connection, to produce a short fall time for a high power pulse.
These solid state switches have many advantages over prior art switches used for similar purposes, for example, spark gaps, thyratrons and SCRs. High power thyratrons are expensive and require substantial heater power; spark gaps are difficult to build and operate at rates over 200 pps, and both of these type switches have limited lives. SCRs cannot handle high peak currents and voltages. Optically activated bulk semiconductor switches can be scaled up in size to increase current and power handling capacity since no p-n junctions are involved.
In the past lasers have been utilized to illuminate solid state switches, however lasers have certain disadvantages, for example lasers do not ordinarily produce pulses of microsecond or more duration at the required intensity for many switching applications. Also the coherent laser beams can be difficult to diffuse uniformly over the gap area. The present invention overcomes these disadvantages with the use of a broadbanded pulsed light source in the form of a flashlamp, coupled with the use of specially processed semiconductor material.